We have noted that a third of 300 patients with melanomas have unusual nevi on their skin in contrast to four percent of normal controls. Only those patients with chronic indolent metastatic melanoma who survive for many years with overt or covert disease develop vitiligo. Melanocytotoxins like phenols, catechols, and hydroquinones have a unique proliferative and stimulating effect on Langerhans cells in the skin of mice. Contact allergens like DNFB and oxazolone do not produce these effects. PUVA, but not shortwave UV light, depletes murine skin of Ia positive dendritic cells, i.e., Langerhans cells. Similarly, cortisone, but not nitrogen mustard, depletes the skin of Langerhans cells.